A list for those who (like myself) read the webtoon with English names and are now a bit confused about who is who:

Eunjang High School

Gray Yeon -  Yeon Shi-eun

Eugene Gale -  Seo Jun-tae

Ben Park - Park Hyu-min

Alex Go - Go Hyun-tak/ Hyeon-tak

Gerard Jin - Jin Ga-yool

Teddy Jin - Jin Tae-oh

Rowan Im - Im Ju-yang

Philip Kim - Kim Pil-young

Colton Choi - Choi Hyo-man 

Byuksan Middle School (Gray's/Shi-eun's former school)

Stephen Ahn - Ahn Soo-ho/Su-ho

Bryce Oh - Oh Beom-seok

Oswald Yang - Yang Seong-chun

Yoosun High School

Jimmy Bae -  Bae Ji-hoon

Jack Kang - Kang Jeong-yeon

Harper Ha -  Ha Hee-cheol

Hugo Yoon -  Yoon Ho-young

Hyeongshin High School

Myles Joo -  Joo Seung-jin

Forrest Lee - Lee Se-han

Sam Lee - Lee Gong-sam

Robin Ha - Ha Min-jo

Ganghak High School

Wolf Keum - Geum Seon-gje

Jared Sun - Seon Jong-won

Hayden Ma - Ma Seok-hee

Daehyeon High School

Jake Ji - Ji Hak-ho

Dean Kwan - Kwon Hyuk-jin/Hyeok-jin

Timothy Park - Park Tae-ghi

Yeo-Il High School

Donald Na - Na Baek-jin

Kingsley Kwan  - Kway Seok-hyeon

Miscellaneous

Lily - Nam Jeon-ga

Lara Lee - Lee Min-ji

Julia Chae - Chae Yoo-jin

Kenny Ji - Ji Gwang-seok

Seems timeline of Gray's/Shi-eun's former school in drama version change from Middle school to Highschool Class 1