Disclosed are various embodiments for modifying network site behavior. At least one session-level performance metric associated with a client is determined. The one or more session-level performance metrics are determined from one or more latency times. Each one of the latency times represents a time elapsed between a sending of a network page request in the client and a rendering in the client of a network page received from a network page server in response to the network page request. A response to a next network page request from the client is modified according to the one or more session-level performance metrics in order to adjust a next latency time for the client.