• algorithmic approach;
  • error correction;
  • ESL (English as a second language);
  • lexico-grammatical errors;
  • second language acquisition (SLA);
  • English

This article reports on the results of a research study that investigated the effectiveness of using an algorithmic approach to error correction to help Hong Kong English-as-a-second-language (ESL) learners overcome persistent lexico-grammatical problems. Ten error types were selected for the experiment, and one set of remedial instructional materials was designed for each error type. The materials were implemented with more than 450 students at both secondary and tertiary levels. Pretests, posttests, and delayed posttests were administered to test the effectiveness of the approach, and a plenary review meeting was organized to gather feedback. The results showed that the approach was versatile and effective and that the students showed significant improvements for the items taught. It is argued that form-focused remedial instruction is effective in enhancing learners' language accuracy in their second language (L2) output.