It can be difficult to find adequate strategies when teaching problem solving in a standard based mathematics classroom. The purpose of this study was to improve students' problem solving skills and attitudes through differentiated instruction when working on lengthy performance tasks in cooperative groups. This action research studied for 15 days whether students in a treatment group (n = 28), who were grouped by learning styles (auditory, kinesthetic, and visual), would display greater ability learning the standards or display better attitudes towards problem solving when compared to a control group (n = 28) who were grouped in random cooperative groups. When the qualitative and quantitative data were analyzed, the results demonstrated that the treatment group did not show significant gains when compared to random cooperative groups. The following are appended: (1) Instructional Unit Plan: Quadratic Investigations; (2) Peer-Review Instructional Plan Rubric; (3) Unit 5 Math I Test: Factoring and Solving Quadratics; (4) Student Problem Solving Attitudes Scale; (5) Performance Task Answer Sheet; (6) Product Grading Rubric; (7) Learning Channel Preference; (8) Learning Style Menu; (9) Note Taking for Reflective Journal; (10) Reflective Journal Prompts; and (11) Learning Style Survey. (Contains 12 tables.)