The task-based approach to second or foreign language pedagogy aims to provide learners with a natural context for authentic language use. While learners are performing real-world or pedagogical tasks, they have opportunities not only to get a rich and comprehensible input of real language, but also to produce target language items to exchange meanings. Interaction in doing the tasks is thought to facilitate language learning process. Thus, one of the important things that teachers have to do first for their task-based English classes is to design tasks for target language items reflecting native speakers’ authentic language use. It is expected that learners can communicate with foreigners using the prescriptive target language items outside the classroom. This research attempted to find out if non-native English teachers would be able to make accurate predictions about target language items in terms of language forms and lexical phrases that would naturally occur when English native speakers carried out two types of tasks (closed tasks and open tasks). The results showed that many language items predicted by non-native English teachers did not appear in the recorded data by English native speakers, especially for open tasks. Thus, this research called into question the practice of setting tasks at the end of a PPP cycle (presentation, practice, and production), to allow students to put into use target language items that has previously been practised.