Use flashcards so that he will have practice physically locating the notes. Even better, flash those cards in a manner that sounds like music, say for example on the Oh Christmas Tree theme. So you would flash G C C C D E E E. Then as he gets better, flash new cards with more than one note on them. Even better, use a metrenome and have him play it to the beat.Then use flashcards that include a bass and treble clef, just one note on each staff. If should also be done in a musica manner. Re-use the Christmas Tree theme but use the bass clef to complement the theme.As for sentence mnemonics, I think they are a complete waste of time as it will not help them play the note any faster. It actually complicates the matter as letters on white and black thingies mean nothing. The only purpose of being able to identify notes by letters ( A - G) are for verbal identification so that when you say C, he knows which key to press. Instead, when you flash those cards, after he plays it , YOU say what note it is. But hold off on this until after he is proficient at locating those keys that correspond to the notes.