Can my son apply for a student visa next year and shift his IELTS score with him in New Zealand?

Yes, your son can use his existing IELTS score for a New Zealand student visa application next year, as long as the score is still valid at the time of application.

IELTS scores are typically valid for two years from the test date. If his score is within this period when he applies, he can use it for both admission and the visa process. If the score has expired, he will need to retake the IELTS test.