Explicit timing and interspersal assignments have been validated as effective methods to facilitate students' math practice. However, no researchers have explored the combinative effect of these two methods. In Study 1, we extended the literature by comparing the effect of explicit timing with interspersal assignments, and interspersal assignments without timing. Generally, participants' rate of digits correct on easy and hard addition problems was higher during the explicit timing condition than during the untimed condition. However, the participants' rate of digits correct decreased after initial implementation of the explicit timing condition. Motivation plays a crucial role in maintaining performance levels and helping students make continuous progress. Preferred reinforcers and setting academic targets have been widely utilized as active motivational components to increase the likelihood of a successful strategy in school settings. In Study 2, we employed a brief MSWO reinforcer assessment to identify individual student's low- and high-preference reinforcers and examined the effects of explicit timing on interspersed assignments combined with high preference or low preference reinforcers, and setting academic targets. In general, explicit timing combined with preferred reinforcers and academic targets produced a more sustainable effect on participants' rate of digits correct than explicit timing alone. In addition, high-preference reinforcers were more effective than low-preference reinforcers for three of five participants. For two participants, an increasing trend was observed when low preference reinforcers were contingent on meeting academic targets. These results are discussed relative to using preference assessments with students with mild/moderate disabilities.