Few studies have gauged the effects of Computer Assisted Language Learning –CALL– on the verbal accuracy of students. The current study explores the use of Hot Potatoes JCloze-type exercises as supplementary classroom work to enhance the English tense accuracy of university students enrolled in three EFL proficiency level courses -high-intermediate (B2) and advanced (C1 and C2). Tense marking was measured before and after a period of autonomous, self-paced CALL work in which students could access theoretical information and practiced with Hot Potatoes exercises. The comparisons revealed that the experience was mainly beneficial for the C1 level course group, the other two experimenting non-significant gains. Results only partially support a boosting effect of CALL additional practice. They also suggest that proficiency should be taken into consideration as it can affect the effect of treatment as not all the proficiency level courses experienced advantages. Alternatives to improve effectiveness are then suggested.