Gradebook

Just to make certain the actions of the aggregations methods are understood in the Moodle gradebook as it appears in 1.95 and greater:

WEIGHTED MEAN: will take the percentage correct for the category or item and multiply it times the weight. If all weights don't add up to 100, it will first scale the weights so all weights DO add up to 100 and use the scaled weight for its calculation.

SIMPLE WEIGHTED MEAN: wil take the total of the points earned times and divide it by the total points EARNABLE to arrive at a percentage.

In your case, the percentage described above in SWM will be acted upon as described above in WM to arrive at the total.

You've likely stumbled on one of the (IMO) MAJOR FLAWS of the current gradebook -- not maintaining accurate category maxes unless SUM aggregation is used. The suggestion to change to SUM aggregation method is useful only if all grades are filled -- if some are not yet completed, the student will be charged as though they received a zero for that grade. Manipulating the category max from the Items and Categories tab will likely bring you to the point of most reliable success. Without a screenshot I'd suggest it needs to be 100 in order for the category totals to come out correct but I can't be certain.