What is the difference between a one-tailed hypothesis and a two-tailed hypothesis?

Both one-tailed and two-tailed hypothesis are examples of alternative or experimental hypothesis, which predict there will be a psychological effect. A one tailed hypothesis, also known as a directional hypothesis, points to what direction the effect will appear in, for example if we were studying whether student's attendance affects their grades, the one tailed hypothesis would be that students with higher attendance will have significantly higher grades than students with low attendance. On the other hand, a two-tailed hypothesis, also known as non-directional, will still predict that there will be an effect, but will not say what direction it will appear in. For example, in the same study a two-tailed hypothesis might look like, there will be a significant difference in the grades of students with high attendance and students with low attendance.A null hypothesis is separate as it says that there will not be a psychological test in either condition.