Fostering peer interaction and shared learning is an important aim of inclusive instruction. However, it has not been established whether it is possible to offer explicit and intensive support for low achievers in inclusive settings. This longitudinal study examined whether a structured program that includes cooperative learning fosters computational competence and flexible strategy use by low achievers in mathematics in inclusive classrooms. 126 persistent counters from 35 inclusive classrooms in grade 2 participated in a structured intervention lasting ten weeks, under three conditions: Cooperative learning (CL, students working in pairs during seatwork), individual learning (IND, students working individually during seatwork) and a control group (CG) with "business as usual." Even when there was substantial class-specific differential development during group-based interventions, between pre- and posttest, results showed no statistically significant main effects for either of the two intervention conditions relative to the control group. However, compared to the CG-group, the CL intervention showed a higher slope for pretest performance, indicating that students with a higher level of computation competence benefited relatively more from the CL intervention than students with similar preconditions in the CG. The results provide evidence that multiple approaches are needed; approaches which combine well-structured programs stimulating cooperative learning and shared learning situations with intensive and individualized measures are of benefit for students with very low mathematical competence.