<p>Planning can be defined as a procedure aimed at achieving a determined goal or solving a problem. Tower of London task (TOL) is one of the most used cognitive tasks for measuring successful cognitive planning. However, error analysis of TOL was not studied enough in child samples. In the present study, a TOL task was administered to a sample of preschoolers from Unsatisfied Basic Needs (UBN) homes. The current study aims to analyze the influence of different problem parameters on TOL’s performance. Such analyses include assessing the number of correctly solved problems, the time required to solve them, and children’s behavior in incorrectly solved problems. Results showed that, while in correctly solved problems, only planning times showed statistically significant differences between with different problem parameters; in incorrect trials, movement times might also be relevant. Different patterns of response time results could show qualitatively different processes in correct and incorrectly solved problems. Higher planning times in correctly solved trials might evidence a pre-planning or look-ahead processing, while higher error movement times in incorrectly solved trials might show a more online-planning process. In conclusion, this study could show the relevance of looking at both correct and incorrect solutions to planning problems, revealing important differences in planning processes and strategies applied by children in order to accomplish a determined goal.</p>