He has no limitations with computation, just language. Luckily, his parents speak a little English and are learning and will teach him. But my grandmother just retired and I thought for the next few months she could come up one or two days a week and work with him at school. I have a few ideas on what she could do, but do you have ANY ideas or activities that come to mind? She will tutor him an hour at a time.

Insist that his parents do NOT teach him English since they do not speak the language properly and correctly themselves and therefore do not have the skills to teach him.
Having his parents teach him is detrimental to his progress.
If he gets English lessons from his parents, he will not pay attention to anything his American/Canadian teachers tell him.
What she should do is liken the English language to math, and then practice problem-solving. For example, a sentence is like addition: subject + verb + object = sentence
or, noun + verb + adjective = ????
Ask him what's missing etc.

The time is coming when every teacher will need to be trained in teaching English language learners. A really great book for you to read to get started is: Reading, Writing and Learning in ESL A Resource Book for K-12 Teachers by Suzanne F. Peregoy and Owen F. Boyle.

It will take many years before this student's academic language skills are well established. (5-8) Be aware that in a year or two (if you still have the student) he will likely appear to be proficient in English because his social language skills will be very good. But in reality, he will likely still struggle to access content taught in English.

In addition to the scaffolding techniques mentioned in the previous answer, try to arrange for him to have as many interactions with English speakers as possible. Language is acquired through interaction. Tutoring is a great support, but the real learning happens when participating in real life interactions.

That said, I'm sure you have opportunities in your math class to do collaborative learning - pair him up with others and make them responsible for completing projects that require math skills and communication skills.

I have training in GLAD (Guided Language Aquisition and Development). A few techniques I suggest are"

Color coding anything written. For example, nouns in red, verbs in blue, etc. Using different colors helps the learner differentiate print concepts.

Another very important idea is to use a LOT of visuals and realia. Use a lot of pictures and real life objects to explain concepts.

Finally, TPR, total physical response is KEY. If you are talking about the body parts, touch each part and the student shold do the same, saying and touching each part. It may seem silly but head, shoulders, knees and toes works across ages groups!

Good luck!