Employ visuals. Post a border along the top of the chalkboard or whiteboard of the alphabet in uppercase and lowercase. Make sure the students constantly see the alphabet in order. Use worksheets in which the students trace or copy the letters (in order) to practice writing them. Have the children arrange letter blocks in order.
Teach the alphabet song; the melody helps children remember the order of the letters and they love to sing. Sing with the whole class together. Recite the alphabet aloud daily. Recite the alphabet to a drumbeat or turn the alphabet into a cheer.
Have the students write out the alphabet over and over. Employ repetition, a proven method for transferring knowledge from short term memory to long term. Vary the activity by having them write all caps one time and all lowercase another and have them write the upper and lower case together sometimes.