failure to meet intellectual standards
sitting, crawling, or walking later than other children
problems learning to talk or trouble speaking clearly
memory problems
inability to understand the consequences of actions
inability to think logically
childish behavior beyond a normal age
lack of curiosity
learning difficulties
IQ below 70
inability to lead a normal life because of the inability to communicate, take care of oneself, or interact with others

Individuals who are intellectually disabled will often have some of the following behavioral issues:

aggression
dependency
withdrawal from social activities
attention-seeking behavior
depression during adolescent and teen years
lack of impulse control
passivity
tendency toward self-injury
stubbornness
low self-esteem
low tolerance for frustration
psychotic disorders
attention difficulties