The 19-year-old captained Albion’s under-23s last season and made an appearance as a substitute in the 2-0 win over Preston last September in the Carabao Cup, his second appearance in the competition after he made his first-team debut against Aston Villa in September 2019.
Aberdeen finished fourth in the Scottish Premiership last season.
Albion’s technical director Dan Ashworth said, “This is a great opportunity for Teddy to take the next step in his development.
“This is the opportunity he needs to play regular first-team football. The Scottish Premiership is probably the strongest it has been for years next season with big clubs like Hearts and Dundee promoted.
“Aberdeen are also in the new Europa Conference League and I’m sure Teddy will relish the challenge of playing regular first-team football.
“We wish him every success and of course we’ll be monitoring his progress carefully during the season.”