Charles Ellicott Commentary 2 Kings 12:2

"And Jehoash did that which was right in the eyes of Jehovah all his days wherein Jehoiada the priest instructed him." — 2 Kings 12:2 (ASV)

All his days wherein Jehoiada the priest instructed him. —The Hebrew is ambiguous, but may certainly mean this, which is the rendering of the Septuagint and Vulgate. (The accent dividing the verse ought to fall on “the Lord” rather than on “his days.”) Perhaps the peculiar form of the sentence arose in this way: the writer first recorded the usual statement concerning kings who supported the worship of Jehovah, and then, remembering the evils which followed the death of the high priest (2 Chronicles 24:17), added as a correction of that statement, “during which Jehoiada the priest instructed him.” Thenius says the words can only be rendered, all his life long, because Jehoiada had instructed him.

They certainly can, however, be rendered as our version renders them, and further, in this way: “And Jehoash did ... all his days, whom Jehoiada the priest instructed.” But the ambiguity of the statement gave an opportunity for discrediting the chronicler.