This study's 1st purpose was to investigate effects of a 4th- and 5th-grade "next-generation" fraction intervention, which included 6 enhancements over a previously validated fraction intervention, designed to address Career- and College-Readiness standards. The next-generation intervention is referred to as "Super Solvers." The study's 2nd purpose was to assess effects of the next-generation fraction intervention at follow-up, 1 year after intervention ended. The 3rd purpose was to isolate the effects of 1 of the 6 intervention enhancements: interleaved fraction calculations instruction. Students with intensive intervention needs were randomized to next-generation fraction intervention ("Super Solvers": SSINT) with blocked calculations instruction (SSINT_B), SSINT with interleaved calculations instruction (SSINT_I), and control. On a mix of proximal and transfer outcomes, SSINT (across) conditions produced strong, significant effects over control at posttest. At follow-up, effect sizes were weaker but remained significant on calculations: g = 1.22. On other measures, follow-up g was 0.39-0.58. The effect of SSINT_I over SSINT_B, although not significant at posttest (g = 0.28), was statistically significant and large at follow-up (g = 0.65), in line with the cognitive science literature showing long-term advantages for interleaved instruction. Results suggest next-generation fraction intervention efficacy for intensive needs students and the importance of interleaved instruction. [This paper will be published in "Exceptional Children."]