As you stated correctly the key would be practice. If the students don´t practice on their own (e. g. for Bar-B-Q or camp fire on weekend trips) their chance for aquiring that skill is pretty slim. Most modern households do no longer require to use a match or a lighter. The only way to build this skill may be to encourage your scouts to try and build a fire on every opportunity. In the case of the kids you may have to convince the parents to allow it.
I know some people who have a hard time when they have to light a fire with perfectly dry fire wood, good kindling, paper, gasoline and a small torch in dry weather with no wind. You have to see it to believe it but it´s reality these days.