Students’ use of standard algorithms for solving linear equations Jon R. Star Michigan State University.
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Students’ use of standard algorithms for solving linear equations Jon R. Star Michigan State University
PME-NA 20052 Acknowledgements Thanks to graduate students at MSU: Kosze Lee, Beste Gucler, Howard Glasser, Mustafa Demir, and Kuo-Liang Chang Thanks to Bethany Rittle-Johnson, Vanderbilt, for her collaboration in the design and implementation of this study. Funds supporting this work provided by small grants from the Michigan State University College of Education.
PME-NA 20053 Starting definitions A procedure is a step-by-step plan of action for accomplishing a task A strategy is a plan of action for accomplishing a task I use these terms synonymously, as is the norm among many psychologists who study strategy change (e.g., Siegler)
PME-NA 20054 More definitions A procedure/strategy can be either: A heuristic, which is a helpful procedure for arriving at a solution; a rule of thumb An algorithm, which is a procedure that is deterministic; when one follows the steps in a predetermined order, one is guaranteed to reach the solution
PME-NA 20055 Standard algorithms For some problems, a “standard algorithm” (SA) exists Called “standard” because it is commonly and often explicitly taught as THE way to solve problems within a problem class
PME-NA 20056 Strategies for 4(x + 5) = 80 A standard algorithm (SA) 4(x + 5) = 80 4x + 20 = 80 4x = 60 x = 15 Alternative approach #1 4(x + 5) = 80 x + 5 = 20 x = 15 Alternative approach #2 4(x + 5) = 80 4x + 20 = 80 4x - 60 = 0 x - 15 = 0 x = 15
PME-NA 20057 SA, more generally 1. Distribute first, to “clear” parentheses 2. Combine like variable and constant terms on each side 3. ‘Move’ variable terms to one side and constant terms to the other side 4. Divide both sides by the coefficient of the variable term
PME-NA 20058 Pros and cons of SA Reasonably efficient Widely applicable Can be executed often without attending to specifics of the problem Are not always the best or most efficient strategy Over reliance on SA may lead to difficulties on unfamiliar problems Ability to use not always connected with why algorithm is effective; may lead to rote memorization; strategy may be easily forgotten
PME-NA 20059 Learning standard algorithms Learning and use of SAs has become a flashpoint issue in US mathematics education Should they be learned at all? explicitly taught? discovered? Not a lot of research on students’ learning of SA to help resolve these issues Particularly on algorithms other than arithmetic
PME-NA 200510 Not researched in high school? Key features of elementary school reform instruction are less typical at high school level: Sharing and comparing of multiple strategies for solving problems Allowing students to discover their own algorithms, rather than providing direct instruction on a SA Allowing students to use non-standard algorithms
PME-NA 200511 Not researched in high school? Discovery of SAs is presumed to be more difficult, if not highly improbable, in high school “Are you saying you want my students to ‘discover’ the quadratic formula?!” As a result, many teachers feel that it is necessary to provide direct instruction on strategies such as the SA “If I don’t teach students this algorithm, there is no way that they would come up with it on their own.”
PME-NA 200512 Unquestioned assumptions Is direct instruction the only way that students will learn the SA? Can students discover the SA largely on their own? When some students discover a strategy and others are shown it by direct instruction, is there a difference in how students use the strategy?
PME-NA 200513 Larger goal: Flexibility We want students to know the SA but also to be flexible in their knowledge of problem solving strategies, meaning that they: Know a variety of other strategies (SA and others) that can be used to solve similar problems Are able to adaptively select the most appropriate strategy (SA and others) for solving a particular problem (Star, 2001, 2002, 2004, 2005)
PME-NA 200514 Research questions Do students discover the SA for solving linear equations when allowed to work largely on their own? Do either of two instructional interventions affect the discovery and use of the SA among algebra equation solvers? Direct instruction Alternative ordering task (Star, 2001) Goal was to see what strategies students develop and how they make sense of, use, and modify these strategies
PME-NA 200515 Method 130 6th graders (82 girls, 48 boys) 5 one-hour classes in one week (Mon - Fri) Class size 8 to 15 students; students worked individually Pre-test (Mon), post-test (Fri); three problem-solving sessions (Tues, Wed, Thurs) Domain was linear equation solving 3(x + 1) = 12 2(x + 3) + 4(x + 3) = 24 9(x + 2) + 3(x + 2) + 3 = 18x + 9
PME-NA 200516 Prior knowledge & instruction Students had no prior knowledge of symbolic approaches for solving equations Minimal instruction and feedback provided 30 minute benchmark lesson Combine like terms, add to both sides, multiply to both sides, distribute How to use each step individually No strategic guidance provided during study No worked examples
PME-NA 200517 Alternative ordering task During problem solving, some students were asked to re-solve a previously completed problem, but using a different ordering of steps (Star, 2001) Random assignment to condition by class Control group solved new but isomorphic problem 2(x + 1) = 10 3(x + 2) = 15
PME-NA 200518 Direct instruction At start of 2nd problem solving class (Wed), 3 worked examples presented to direct instruction classes “This is the way I solve this equation.” Each problem solved with using a different method; one was the SA Total time was 8 minutes of supplemental instruction Random assignment to condition by class
PME-NA 200519 Analysis Students’ written work was analyzed for use of SA Booklet problems (Tues, Wed, Thurs sessions) - total of 31 equations attempted Post-test problems - total of 9 equations attempted Three “markers” of SA: Distribute first Combine like terms before moving Divide as a final step
PME-NA 200520 Results. About 2/3 of students did not discover SA Of those who did, a small number started using SA very early
PME-NA 200526 Results...... Stated somewhat differently (and not including 12 Early Users): 25% (16 of 65) of students in the Direct Instruction condition used SA on the post- test 30% (16 of 53) of students in the Discovery condition used SA on the post-test
PME-NA 200527 Results....... The alternative ordering task made it less likely that a student would use the SA on the post-test (p <.05) Alternative ordering task made it more likely that students would use other, more efficient or innovative strategies than the SA on the post-test
PME-NA 200529 Summary of results. Do students discover the SA for solving linear equations when allowed to work largely on their own? Most did not Only about one-fourth of students learned the SA on their own Is one-fourth high or low?
PME-NA 200530 Summary of results.. Do either of two instructional interventions affect the discovery and use of the SA among algebra equation solvers? There was no difference in the rate of SA use between the direct instruction and discovery conditions The alternative ordering condition made it less likely that students used the SA on the post-test
PME-NA 200531 Implications for SA learning Neither a short period of direct instruction (viewing of worked examples) nor pure discovery was particularly effective in promoting development of the SA Is learning the SA a goal of algebra instruction? If so, how should it best be taught?
PME-NA 200532 Implications for flexibility Flexibility aided by activities such as the alternative ordering task, where students generate and compare multiple strategies for solving procedural problems Direct instruction did not improve chances of discovering the SA, so activities such as the alternative ordering task appear to be a win- win proposition
This presentation and other related papers can be downloaded at: www.msu.edu/~jonstar Jon R. Star Michigan State University email@example.com