I can related to your story very well. I lost count on the number of kids that I have had over to my house and\or ball field for free lessons to work on a weakness they had. More often than not, these weaknesses were centered around the mental side of the game (80% of the game at this age in my opinion), and most all of these extras were on non-practice days. There just isn't enough time to work with individual players (the quality time it requires to really make improvements) during our regular allotted practice time during the season.
How a player responds to a great play is easy, how they respond to a called 3rd strike or ball through the legs is another story.
One of the things that I do (and my top 3 players enjoy doing) is to let them work with the weaker players some time during the practice. Doing this really grows a players confidence in leading, and forms a friendship that is not athletic or performance base with the weaker players.
My son worked with a weaker player on bunting one day, and I overheard him say, "my dad says to square when the pitcher makes his move, but that doesn't work, wait till he releasing the ball, and you will catch everyone back on their heels" he's was only 9 when that happened and I laughed the whole practice