Well if you are looking at this as a learning opportunity as well as an investment, tell him to make an investment plan himself.
A low cost ETF is a sensible investment but there is not much to learn.
The Motley Fool is an excellent website to learn from.
Maybe decide to pick 10 shares, to invest in. Challenge him to explain what his reason for each one is.
The kind of info on business channels is very news driven, its fine for someone with an understanding of the fundamentals.
Benjamin Graham's "The Intelligent Investor" is still the best guide to investing, a bit much maybe for a 13 year old, but you never know.