The March/April edition of
ISTE's journal
Learning and Leading with Technology includes a list of several mobile apps that might be appropriate for middle school life science or high school environmental science. These are mostly fieldwork and outdoor observation apps; some of them are designed specifically for kids, but others are part of collaborative "crowd-sourced" observations to aid researchers. All of the apps listed here are completely free.
Available for iOS and Android:
Available for iOS only: