Abil, native speakers NEVER use a that-clause after "want." You should say, "I want you to become more attentive." In fact, perhaps it might be better to say "to be" more attentive. Native speakers do, however, say (in formal speech), I demand, order, insist, advise, ask, command, request THAT you be more attentive. This is called the subjunctive. If you post a question requesting more informa