A study investigated the effect of Frank O'Hare's "Sentencecraft" sentence combining program on the written syntactic skills, reading comprehension level, and speed of average ability ninth-grade students. The sample consisted of 75 experimental group students and 68 control group students. Following a pretest, the experimental group received 9 weeks of practice in combining kernel sentences into more complex and mature syntactic forms. For the remainder of the 16-week experimental period, both groups wrote six argumentative compositions at 2-week intervals, except for essay two, which was written 3 weeks after the pretest. The six compositions were scored by counting the total number of words, words per T-unit, words per clause, and clauses per T-unit. Reading comprehension level and rate were measured by the Davis Reading Test. A posttest was administered after 16 weeks, followed by a delayed posttest 8 weeks after that. No significant mean increases were found across the six writing occasions as a result of the "Sentencecraft" program. Differences in mean reading comprehension level scores of both groups were significant between pretest and delayed posttest, with no significant differences on testing occasions, suggesting that the experimental treatment was not effective in improving students' level of comprehension. Nor did the experimental group show a significant mean increase in "speed of comprehension" between pretest and delayed posttest. (HTH)