This study aimed to investigate the impact of textual enhancement and metalinguistic explanation as focus-on-form tasks tending to encourage the acquisition of nominal clauses (NCs) in English. It explored (a) whether textual enhancement and metalinguistic explanation would promote and enhance the knowledge of NCs, (b) whether these two tasks would differ in terms of enhancing learners' knowledge of nominal clauses, and (c) whether learners' use of self-regulatory capacity for grammar acquisition would have differential effects on textual enhancement and explicit explanation groups. A test of recognizing noun clauses and a test of producing combined sentences were used as both the pretest and the posttest to measure the achievement of first-year undergraduate university students in four intact classes. A grammar self-regulation questionnaire was also administered to measure the use of self-regulatory capacity. The findings demonstrated that both textual enhancement and explicit instruction contributed to developing grammatical knowledge of the learners at both recognition and production level. The results also showed that the learners who received textual enhancement used their grammar self-regulatory capacity more effectively in developing their receptive knowledge of NCs. It can be concluded that textual enhancement, which provides learners with less explicit instruction, pushes them to use their self-regulatory capacity more effectively in improving receptive knowledge of grammar.
