"Teachers should be careful to give the students what they most need, instead of allowing them to take what studies they choose. They should test the accuracy and knowledge of the students; then they can tell whether they have reached the heights to which they think they have attained. CT 216.2"
"Prove all things; hold fast that which is good."
The verse from 1 Thessalonians encourages testing and discernment, which aligns with EGW's call for teachers to assess students' understanding. However, the connection is not overwhelmingly strong, hence the slight reduction in confidence.
"Let the students be made to understand that God has given to everyone a wonderful mechanism—the human body—which we are to use to glorify Him. The powers of the body are constantly working in our behalf, and if we choose we may bring them under control. CT 216.5"
"For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God’s."
The EGW passage directly echoes the sentiment and wording of 1 Corinthians 6:20, emphasizing the glorification of God through the body. It's more than a principle; it's a clear allusion.