Vowels in Farsi

In Farsi we don’t have vowels. We have some symbols to indicate the sound of them but it is not usually written in a text. & only first-graders use those symbols; so most of my students thought that using A, E or I is not necessary.... it took me some time to teach them to write the letters properly. Last time they had diction I reminded them to "use the vowels". The result was good except one of my students who wrote the Farsi symbols instead of the letters!