This article reports on a national survey of complementary school providers in Scotland to gain insights into their perspectives of the abrupt transition to online learning spaces during the COVID-19 pandemic. Data gathered from a questionnaire (n=34) and in-depth interviews (n=13) covering 19 different heritage languages are analysed through the lens of practical evaluation, projective agency, and the concept of uncertainty in education. While teacher agency has been a subject of recent study and debate, there is limited research on enacting agency in complementary school settings. The study draws light on the ways in which school leaders enacted agency on multiple levels and in complex and nuanced ways as schools adapted their diverse provision in the face of challenges triggered by COVID-19. Findings reveal that (i) closure of school sites led to further pressures for schools and for the learners, families, and communities that they support, and (ii) the creation of online spaces provided opportunities for complementary schools to explore new resources, facilitate innovative forms of learning and teaching, and extend the reach of their school. We conclude with consideration of new avenues for complementary school planning and provision, and implications for developing online learning spaces for heritage languages.