School glue will wash out pretty easily. It's the gunk that stuck to the glue while it was drying that can give you a problem. Use a spoon to gently peel away any glue that you can.
Removing that top layer should peel off whatever stuck to it. Then launder the item in warm water to remove the remainder of the glue.
Marker stains can usually be removed with some rubbing alcohol. Put some paper towels between the layers of fabric and dip a cotton ball into some rubbing alcohol. Dab the marker stain, as the marker transfers to the cotton, switch to a new cotton ball and repeat until no more marker transfers. Then, wash the item in coolwater in a regular cycle to remove the rest of the stain.
Fingerpaints are another common school stain. If the stain has dried start by wetting it with cool water. Then make a paste of warm water and baking soda and work the paste into the stain.
You'll see the paint start to separate from the fabric. Once it does, wash the item in cool water to remove the remainder of the stain!
School stains conqured! I'm Mrs. Fixit and it's just that simple!