Always check the app/game before using it with students.

Apps Matrix K-12
Please note- this is a guide ONLY. Some of these apps might apply to more than one subject area and also across grade levels .
More Apps - with links to Apps store

Problem solving apps - just a start
Robo Logic
Sim city
Oregon Trail
Jelly Car 1 & 2
Diamond Islands

App Reviews by Grade Level from iEAR Blog

Kindergarten Apps
Early Years Apps
Late Elementary Apps
Middle School Apps from iEAR blog
High School Apps

From Louise Duncan

Apps I use with Students

Apps finders and reviews

Apps Shopper - apps for education category
iEAR Blog- i Educational Apps Review (good information)
iEAR video casts - apps reviews
Lists of iPhone apps for education seems to be updated regularly
100 Most Educational iPhone apps - for high school and college students mainly
Cool iPhone Apps Free to $5 Caps blog