Every few envelopes they jammed or carried through the printer incorrectly. This made quite a mess. If you want to use inexpensive envelopes for mass mailings then I suggest you print labels . If you are using a Laser rpinter you must get envelopes and labels specifically for them. The heat the printer uses will seal or unglue incorrect media.
Labels can come off the sheets and clog up the printer.
Page Setup to set the envelopes orientation to horizontal. Save the envelope template. Do not close it. Open the database of names and addresses you will be using. Find to search the school database by the teacher's name for those students.