The governing body assessed the facility at Auchenhowie as part of their 2013/14 Club Academy Scotland audit.
And a grant is issued that corresponds with the rating - meaning the Gers will receive the maximum amount.
Speaking to the official Rangers website, Sinclair said: "We are delighted to have achieved six-star status. It's a great compliment to the standards we set.
"Having this status certainly won't do us any harm. It's nice to be recognised as being there as the best in the country.
"After everything which has happened at the club in the last couple of years, it's good that people get a reminder of that.
"We're making progress. There are young players in our system who will benefit from the environment here at the club."