This study brings together previous research on writing processes and Spanish heritage language (SHL) learners to obtain a clearer picture of these learners' writing behaviors in English and Spanish. Following a cognitive-oriented framework, the study explores planning time, execution time, monitoring time, accuracy, and fluency. Twelve SHL learners in a third-year Spanish class at a university in the US Southwest participated in the study. Screen-capture software recorded their behaviors while they responded to similar prompts in Spanish and English. Results indicated that participants spent significantly more time planning between sentences in their Spanish responses. Nevertheless, they showed more fluency (word output, mean sentence length, and words per minute) and accuracy in English than in Spanish. These findings, along with the participants' more limited experience with academic writing in Spanish, suggest that SHL curricula should draw upon any previous Spanish writing experience students may have had and move from informal to more academically oriented assignments. (Contains 6 notes and 5 tables.)