Stem-changing verbs:
O:UE http://www.studyspanish.com/lessons/stemue.htm NOTES
http://www.studyspanish.com/practice/stemue.htm
E:IE http://www.studyspanish.com/lessons/stemie.htm NOTES
E:IE http://www.studyspanish.com/practice/stemie.htm
E:I http://www.studyspanish.com/lessons/stemi.htm NOTES
E:I http://www.studyspanish.com/practice/stemi.htm
https://conjuguemos.com/activity.php?language=spanish&id=2&source=public&type=verbs Conjugation trainer
https://conjuguemos.com/activity.php?id=2&source=public&language=spanish&type=fillin
https://conjuguemos.com/activity.php?id=3&source=public&language=spanish&type=fillin
http://www.spanishdict.com/topics/practice/38
https://personal.colby.edu/~bknelson/SLC/presente_stem_change.php
https://personal.colby.edu/~bknelson/SLC/presente1.php
http://www.proprofs.com/quiz-school/story.php?title=stem-changing-verbs-quiz-1
https://quizlet.com/29131196/los-verbos-del-zapato-e-i-conjugaciones-flash-cards/
https://quizlet.com/29131104/los-verbos-del-zapato-o-ue-u-ue-conjugaciones-flash-cards/
https://quizlet.com/29131288/verbos-del-zapato-e-ie-conjugaciones-flash-cards/