The aim of the present study was to investigate those factors influencing performance in solving story problems in a web-based environment. A situational simulation, "Hiking across Estonia," was explored by two samples of voluntary groups of students, comprising 65 and 50 groups, respectively. They solved 25 ecological and environmental story problems and filled in a pre-test and post-test that evaluated problem-solving skills. The groups were clustered according to their characteristics and performance into five clusters: "slow learners,""quick learners,""successful learners,""smart learners," and "ineffective learners." The clusters were provided with different types of supportive notes and the sequence of problems was rearranged according to the students' initial results in the first four problem-solving tasks. These treatments demonstrated statistically significant improvements in the outcome in solving story problems in small groups. The main factors determining the effectiveness of problem solving were: (i) time spent on learning; (ii) initial skills in problem-solving; (iii) the presence of support in enhancing situation awareness; (iv) graduated problem tasks sequenced on the basis of complexity and difficulty; (v) ratio of genders in a learning group. However, the importance of these factors depended on the cluster and, therefore, it can be concluded that the design of problem-solving instruction has to be adapted according to the clusters' characteristics. (Contains 4 tables and 4 figures.)