Dalla Valle, who has netted twice since initially joining Cherries from Fulham for a month, yesterday extended his stay until the end of the season.
The 19-year-old striker will be available for the final 10 league games of the season and would also be permitted to feature in any potential play-off matches.
Dalla Valle, who has been nicknamed Van Man by his new team-mates, will be looking to continue his impressive form at Carlisle on Saturday.
Fletcher told the Daily Echo: We brought him in to score a couple of goals and he has done that. He has done well and we were keen to keep him for the rest of the season.
We spoke to Fulham and then spoke to the Van Man to ask him if he would be interested. He said he would so all parties were happy.
He had never played at this level before he came here. You need to get used to the pace of League One and he has scored a couple of outstanding goals.
With a few games behind him, he is going to know what it is all about.
It is not just about scoring goals in our team because there are a lot of other things to consider.
There are a few things he is still getting accustomed to but he is a willing lad and very keen to learn. He is going to be a great attribute to us.
Meanwhile, Cherries' striking resources received another fillip yesterday when long-term injury victim Steve Lovell took his first steps on the comeback trail.
Lovell, who has yet to feature since joining Cherries in the summer, came through 45 minutes of the reserves' 2-0 defeat by Swindon.
Fletcher said: We watched Steve in training about 10 days ago and he was a bit tentative. We thought it might be two to three weeks before he played but he has come back ahead of schedule.
I know what it is like when you come back after being out for a while. But you get more confident every day and it will be a huge plus to have Steve back when he is ready.
We don't want him to run before he can walk. We know where he has been and nobody will be pushing him to do anything too soon.
Mark Molesley may require a scan after turning his ankle during the first half, while trialist Calum Butcher is expected to be invited back after impressing Fletcher and boss Lee Bradbury.
A strong Swindon team coasted to victory thanks to goals from Elliott Benyon and Billy Bodin.
Cherries: Murphy, Nelson, Purches, Stephenson (Wakefield, h-t), Butcher, Partington, Makoni, Molesley (Parsons, 26), Lovell (Maybury, h-t), Taylor, Hester.