According to reports, the schools were prohibited for their involvement in examination fraud.
According to PM News, the Ministry of Education of the River state has forwarded the letter de-recognising the impacted institutions to their proprietors.
According to information obtained by Twistok.com, the letter was signed by S.D. Kum, Deputy Registrar/Zonal Coordinator for Head of National office of West African Examinations Council (WAEC). According to Kum, until further notice, all schools affected by the prohibition would not register applicants for the examination.
Some schools in the state have developed the distinction of being known as "Miracle Centres" where all types of exam cheating are permitted, as reported by PM News.
It was learned that desperate candidates and their parents frequent the "wonder centres." See the whole list of prohibited schools below:

Private schools;

1. Rehoboth Int'l Secondary School
2. EL-Olam global academy, Ogbogoro 
3. Nonwa Midland Int'l Christian Sec. Sch,
4. Christ Secondary School,
5. Aboada John Wesley College, Bori
6. Port Harcourt Charry Compre. Sec. Sch,
7. Port Harcourt Rootway Compre. College,
8. Port Harcourt Sonny Memorial College,
9. Port Harcourt Millennium High School,
10. Diobu Sit-up International School,
11. Oyigbo Excel Comprehensive College,
12. Okrika Victory High School,
13. Ogale Nchia Eleme Baptist Vocational College,
14. Oyigho Rich-Model Secondary School,
15. Port Harcourt Atlantic Heralds High School,
16. Asarunia Nobsams International School,
17. Igbo Etche Unique International Secondary School,
18. Etche Ranjenny's High School,
19. Port Harcourt Nigerian Christian Comp. College,

Note: The remaining two schools on the list are not visible in the document published by PM News.

Public schools;

ALSO READ:

Scholarship Program for the Francophonie in Canada 2023.

1. Community Secondary School,
2. Baranyowa Dere Community Secondary School,
3. KONO Boue Community Secondary School,
4. Ido Community Secondary School,
5. Joinkrama Western Ahoada County High School,
6. Kono Community Secondary School,
7. Ban-Ogoi Tua-Tua Community Secondary School,
8. Kpean Comprehensive High Shool,
9. Ahoada Community Secondary School, Ebubu Eleme
10. Baen Comm. Secondary School.
11. Ngo-Uyeada Community Secondary School,
12. Sii Khanna Kono Secondary School,
13. Korokoro Joinkrama Girls' Secondary School,
14. Abam-ama Community Secondary School,

In the meantime, the state government of Rivers has revoked the licenses of the 21 private schools prohibited by WAEC. Professor Kaniyi Ebeku, the state's commissioner for education, announced this on March 21. According to Ebeku, at least 14 public secondary school principals were demoted by the state government after a series of investigations implicating them in WAEC cheating.