"When working with young players, always use a lower rim. ALL experts agree that it's a huge mistake to use a 10 ft. rim. In most cases, an 8 ft. or 9 ft. rim is the way to go. The biggest problem with kids today is that they use a full-sized ball, 10 ft. rim, and they have to "chuck it" to get the ball there. This is where many players establish wrong habits in their basketball shooting form. These habits often linger and hamper players well after they are strong enough and big enough to shoot properly at a ten foot hoop. Getting rid of these habits takes a lot of time and effort, much more than is needed to establish correct habits in the first place. So our advice is simple…
• USE 8 FT. RIMS FOR KIDS THAT ARE 8 YEARS OLD AND UNDER.
• USE 9 FT. RIMS FOR 9 AND 10 YEAR OLDS.
• USE REGULATION FOR 11 YEAR OLDS AND UP.
We also suggest that you use smaller basketballs. For kids 8 and under you can use mini-basketballs (7" in diameter). You'll notice that their shooting form makes an undeniable improvement with the smaller ball. For 9 and 10 year olds, you can use a junior ball (8.75" in diameter), and 11 year olds can use a youth ball until they get to high school.
Source: http://www.breakthroughbasketball.com/fundamentals/shooting/youth-shooting-adjustments.html

Public school approach:
All of the local public schools use 8.5 ft baskets at 3/4 with the exception of 4th grade boys travel teams which play at 10 ft. Most towns have baskets that are height-adjustable. The towns that don't use a basket attachment which lowers the basket to 8.5 ft. I recently attended a 3/4 girls game at Byrd Elementary in Glen Rock. Byrd uses the basket attachment. There was much more scoring in that game than in the 3/4 games in our league, which are typically in the single digits/teens in a 32-minute game. I wasn't keeping track of numbers but the scoring frequency seemed similar to a well-played high school or college game; there was good flow to the game and it was more entertaining to watch because there wasn't long stretches between scores. The game at Byrd was more instructional than competitive -- they didn't keep score and the teams met at half court at the start of quarters to assign man-to-man matchups (as an aside, BreakthroughBasketball.com thinks developing players should not play man-to-man defense; Glen Rock apparently agrees). More information from the Glen Rock league commissioner Steve Kozuch:

"Both the boys and girls rec programs have been playing on 8.5 hoops and in the Byrd and Hamilton gyms since I have been involved with GRYBL (est. 2005). There has never been debate as to how girls program is run as you state below. Very instructional. In the later part of the season, we will get a referee to make sure the girls are learning from their mistakes. Same for boys, first few weeks are instructional, with refs added later in season. There has been debate about 10ft v. 8.5 ft hoops for Boys 3rd /4th program. I put it out for vote last season and majority decided in favor of 8.5ft. The boys travel program begins at 4th grade and plays on 10 ft. hoops. The consensus is the rec program should cater to all players of all ability levels. Therefore, 8.5 ft helps for those children with a very basic level of skill, and recreational program is for both fun and learning.

Basket-attachment at Byrd School
Coaches create best man-to-man matchups after substitutions
Byrd's gym is smaller than a regular gym but the normal baskets are 10ft
Attachment is quickly removed with one-lever and no tools

AOL approach:
AOL is currently the only school in the Parochial league that fields a 4th-grade-only team at the 3/4 level. Third graders at AOL participate in a development program using lower baskets. From Steve Kenny, the commissioner at AOL:

"We have a clinic for third graders Saturday Mornings 10-12. We emphasize drills/games that teach fundamentals and we break it down to 4-5 stations. We keep it moving and fun and limit scrimmages to the last 15-20 minutes. We start the baskets at 8 ft and by the end of the season we set them at 9. Focus on form."

Recommendation:
Steve Kenny at AOL said he would reintroduce the subject at the end-of-season meeting. If we're not successful at getting the Parochial League to lower the baskets for 3/4 -- in-line with the public schools and all published experts on the subject -- we should adopt the AOL model so at least our 3rd graders will be using age-appropriate equipment.