how do I get pen marks out of dd's school shirt?

[MaxandRuby]

this is the 3rd time dd, who has just started reception, has come home with black felt pen marks on her top. One big mark was on her back - goodness knows how it got there, she wasn't telling! It wouldn't come out properly but not so bad as the dress covers it. Today her shirt has pen marks on the front. I'm trying Vanish but it doesn't seem to be shifting. Any ideas? I don't want to have to bin it!

[glitterchick]

Stain Devil.