Here are the science test scores from Ms. O'Donnell's class:

To find the Mean Absolute Deviation (MAD), follow these steps:

1. Find the mean of the data set:
(55 + 60 + 70 + 70 + 75 + 75 + 75 + 80 + 80 + 85 + 85 + 85 + 85 + 90 + 90 + 95 + 100) / 17 = 80

2. Find the absolute deviation from the mean for each data point:
|55-80| = 25
|60-80| = 20
|70-80| = 10
|70-80| = 10
|75-80| = 5
|75-80| = 5
|75-80| = 5
|80-80| = 0
|80-80| = 0
|85-80| = 5
|85-80| = 5
|85-80| = 5
|85-80| = 5
|90-80| = 10
|90-80| = 10
|95-80| = 15
|100-80| = 20

3. Find the average of these absolute deviations:
(25 + 20 + 10 + 10 + 5 + 5 + 5 + 0 + 0 + 5 + 5 + 5 + 5 + 10 + 10 + 15 + 20) / 17 = 147 / 17 = 8.647

Therefore, the Mean Absolute Deviation (MAD) for Ms. O'Donnell's class' science test scores is 8.647.