Scheduling of practice to create a spacing effect has been observed to lead to superior retention of L2 vocabulary and grammar. Two of the various methods of scheduling L2 task practice discussed widely in recent times are interleaving and blocking. In a desirable difficulty framework, both of these methods have been recommended for task repetition practices aimed at learning L2 vocabulary and grammar. Used at the appropriate level of difficulty both have been observed to facilitate the automatization and proceduralization of linguistic knowledge. Keeping two groups of 44 Indian adolescent English as L2 learners under interleaved and blocked conditions during a three-month-long task repetition practice program, the present study attempted to measure the difference in the effect of interleaving and blocking on the retention rate of English vocabulary and grammar. No statistically significant difference in the effect of these two methods on the retention of English vocabulary and grammar was recorded in a repeated measures ANOVA test (p=0.17, F=2.05, d=0.09) conducted on the pre-test, intermediate test, and post-test scores of the participants. Both groups continued to demonstrate limited flexibility and appropriacy in word choice and rare instances of complex forms and structures of sentences in English throughout the three tests.