1. Total score of the initial group:
* Initial average score: 87.3
* Number of initial students: 58
* Total score of initial group: 87.3 * 58 = 5063.4
2. Total score of the second group:
* Average score of second group: 90.7
* Number of students in second group: 12
* Total score of second group: 90.7 * 12 = 1088.4
3. Total score of all students:
* Total score of all students: 5063.4 + 1088.4 = 6151.8
4. Total number of students:
* Total number of students: 58 + 12 = 70
5. Average score of all students:
* Average score of all students: 6151.8 / 70 = 87.88
Therefore, the average score for all 70 students is $\boxed{87.88}$.