Both of my girls best has been 100% and the lowest in the 60s. When they were younger, like 5-7 years old, their numbers were not very consistent. Usually in the 70-80s range. I am so happy that they were not treated based on the PFTs, only symptoms<img src="i/expressions/face-icon-small-smile.gif" border="0">
And even though they seem to culture more now, and one has more lung damage than the other, they both blow in the 90-98% range. Their numbers consistently went up for months as they got better with the technique. I would say that they started blowing GOOD numbers at around the age 8.
But all kids are different. That was just our experience.
We did practice at home with those Blo Paint Pens. The kids had a blast blowing paint out all over the paper, not even knowing they were practicing!
Actually, the one with lung damage is a few points higher (and has never cultured PA) than her sister (who does culture PA)! Go figure. But, I am happy that they finally have consistent numbers and I am confident now when they do the test that the numbers are true indicators at what is going on. It seems like it took a long time to get there!