In this paper, we present our experiences in using two automatic assessment tools, TRAKLA and TRAKLA2, in a second course of programming. In this course, 500-700 students have been enrolled annually during the period 1993-2004. The tools are specifically designed for assessing algorithm simulation exercises in which students simulate the working of algorithms at a conceptual level. Both of these tools allow students to resubmit their solutions after getting feedback. However, the resubmission policy has changed considerably during the period. Those changes reflect the students performance in the exercises. We conclude that an encouraging grading policy, i.e., the more exercises they solve the better grades they achieve, combined with an option to resubmit the solution is a very important factor promoting students' learning. However, in order to prevent aimless trial-and-error problem solving method, the number of resubmissions allowed per assignment should be carefully controlled.