Enhancing student engagement and achievement in large undergraduate university courses is a vibrant area of research. Many existing studies have demonstrated the capacity of technologically enhanced formal and informal learning spaces to promote learning. However, this literature is dominated by studies that use assessment to incentivise student participation, usually in the form of awarding or deducting coursework marks. Our study presents an alternative to this "carrot and stick" approach. We describe the design and implementation of two optional, non-grade-bearing learning support initiatives in a large enrolment, first-year human biology course: first, an online mock test that allows for timely feedback; and second, peer-teaching and--learning using the Piazza discussion platform. We analysed the uptake of these initiatives across three consecutive course offerings (2013-2015), and conveyed to students their potential impact as a series of graphs in the course materials. Regression analysis identified a positive correlation between participation in the mock test and summative achievement in the course for Grade Point Average (GPA)-matched student pairs, with the benefit being most pronounced for students with low-to-middle GPAs. Modelling revealed four different levels of student participation in Piazza, with increasing participation correlated with greater achievement, particularly for students with low-to-middle GPAs. The benefits of the two initiatives were complementary. Interestingly, for certain students, 'passive' participation in Piazza yielded similar learning benefits to 'active' participation, suggesting that active participation is not an antecedent for learning gains. This finding has important implications for instructors who currently require students to 'visibly' engage to earn participation marks.