Propositions need to be more verifiable. The need to be an adequate number of cases, the cases must be representative and consistent with other beliefs. Most middle school students learn about the connection of sperm and egg and the stages of pregnancy. However, to a biologist, that explanation may not be adequate. In the math and science fields, criteria for a good explanation is highly dependent on quantitative data and observation.
Visible evidence is important.
In science the scientific method is a set process for retrieving needed data. In math, proofs are used to confirm ideas. A problem exists here with the fact that science and math are based on theories and subject to change. However good explanations can still be created. One example of this is in the subject of physics.