An experimental group is the group in an experiment that receives the variable being tested. One variable is tested at a time. The experimental group is compared to a control group, which does not receive the test variable. In this way, experimental groups are used to find answers in an experiment.
1 At around 9 months of age, babies begin to pull themselves up to a standing position. 2  By 10 months of age, a baby should be able to grasp objects with thumb and forefinger.
Generally by around three months old laughter should be quite common for most babies and by four months, a baby should be laughing out loud, chortling, giggling and squealing but, as in everything, babies develop at their own rate and there is nothing to worry about if your baby is slower to develop than others.