You will need four local variables, the highest and lowest score, each initialized to 0 and the names of the student's with the highest and lowest scores. Then read through the file and compare the score to the highest existing score. If it's higher, store that student's name and score as the new highest. Do the same with the lowest. Then output the highest and lowest to the output file.

As far as how to develop it, be sure to do it on piece at a time as it's much easier to test and debug. I would reccomend writting the code to read in the file. Then write the code to find the highest score. Then the code for the lowest. Finally, write the code to generate the output.