Task execution duration depends on the employee who performs the task. Specifically in IT projects, an experienced employee can perform assigned tasks several times faster than a novice worker can. Preparing the schedule, project manager should take into account individuals’ productivity determined by analyzing historical data of tasks implementation. Consequently, measured productivity is used in preparing the schedule in an optimal manner (minimizing the time needed to complete project tasks by a team of workers with different skills). As an extension of previous studies the authors formulate a linear programming problem including the possible cooperation of employees with tasks execution. The result of the conducted research is a complete package supporting project managers in determining productivity and scheduling.