This study investigates heritage language (HL) and second language (L2) learners' attitudes and perceptions of their mixed HL-L2 interactions. As part of the activities of a 10-week course, eight Spanish HL learners and 10 L2 learners worked in mixed dyads to complete a series of collaborative writing tasks designed to leverage their complementary strengths and weaknesses. A beginning-of-quarter and an end-of-quarter questionnaire were administered. Learners' responses revealed that HL and L2 learners alike had a highly positive experience that changed their initial reluctance toward collaborative writing. Most learners noticed language gains and an improvement in their writing skills. Yet both HL and L2 participants agreed that L2 learners, who were generally perceived as less proficient, benefited more. HL learners also reported affective benefits from their role as linguistic and cultural experts. Although some challenges were noticed, overall, findings support the use of collaborative writing tasks in mixed classes.