Jehoshaphat fulfilled the Lord's command to teach the law (Deuteronomy 5:1; 17:18–20). He appointed five royal officers, nine Levites, and two priests to teach the people the book of the covenant. Levites often served as teachers during the Second temple period as well (Nehemiah 8:7).
Some versions leave out Tob-adonijah; this seems to be a scribal error of repetition.