Suppose I have a dataframe `df` looking like

```
    school   score   student_id
0    1        100.0   965
1    2        64.0    1483
2    2        100.0   1055
3    2        68.0    1806
4    1        100.0    971

```

I want to find how many maximum scores in each group and get something like this:

```
school count_max
  1       2
  2       1

```

How can I do it?