The main objective of HeLA is to understand why heritage speaker (HS) grammars develop the way they do, by focusing on the severely understudied population of pre-teenage heritage speakers of Spanish. Instead of taking the more traditional approach of comparing heritage speakers to monolingual controls, I focus on individual differences between speakers, and to what extent extra-linguistic factors such as use and exposure of the HL can explain those differences. In addition to input quantity, this project also examines the role of input quality by focusing on cross-generational attrition: the situation where HSs’ parents might exhibit changes in their L1 use which get passed on to the next generation of HSs. I approach this issue by establishing a one-to-one connection between the child heritage speakers and their parents. Moreover, I ask to what extent cross-linguistic influence from the societal language plays a role, by comparing heritage Spanish in two different linguistic contexts in Europe – the UK and The Netherlands – and looking at phenomena that are instantiated differently in English and Dutch: grammatical gender and subject expression. I furthermore combine behavioral and online measures of competence to examine whether the type of task brings anything to bear on the participants’ performances.