I would say the answer lies in attitude. I realise it is never that simple but the UG is constantly at work, so even if children aren't speaking in an L2 classroom is could be because of a lack in confidence in their ability, or just a general dislike or aversion to the language being taught. Generally speaking if a participant's UG is not developed enough in either their first or second language then they will struggle in most L2 tasks.
The universal grammar is something that's widely accepted and is expected to be heard of from general audience. When students are engaged in a L2 classroom they are unsure if the languages have similar grammatical bases or not. Also, their skills might not be affluent to the particular L2 classroom. This is an effect of partial or incomplete Second language (L2) learning.
Notably, the fact whether UG is accessible to L2 learners or not has very little to do with L2 speaking . Reluctance to use L2 is an important issue which teachers should consider.The language teachers should try to train their students in using language learning strategies, and to achieve this end, they should learn about the students, their interests, motivations, and learning styles. The main goal in post modern era should be to help learners to develop liberatory autonomy so that they are able to set their own directions for attaining the targeted goals.
By definition, universal grammar is something all humans are all born with, it therefore cannot be related to differences in language learning behaviour.
Avoidance itself is a strategy in interactions based on language. Psychological factors such as readiness, self-confidence, language ego, willingness to communicate are some internal factors affecting the use of a language. The classroom atmosphere including the peer-relations and teacher-student(s) rapport, power distribution are also some other external factors. You are kindly recommended to refer to R. Ellis's seminal book on Second Language Acquisition 2009. A student may have developed the UG parameter yet be unwilling to communicate due to personal, interpersonal or/and socio-cultural impediments, whether imposed externally or subconsciously.
Avoidance itself is a strategy in interactions based on language. Psychological factors such as readiness, self-confidence, language ego, willingness to communicate are some internal factors affecting the use of a language. The classroom atmosphere including the peer-relations and teacher-student(s) rapport, power distribution are also some other external factors. You are kindly recommended to refer to R. Ellis's seminal book on Second Language Acquisition 2009. A student may have developed the UG parameter yet be unwilling to communicate due to personal, interpersonal or/and socio-cultural impediments, whether imposed externally or subconsciously. Moreover, the improper use of the mechanism of IRF (initiate, Respond, Feedback) format as the common move in classroom discourse can be a demotivating factor in some class-bound interactions.