(わたしは)きのう　小林さんは　がっこうを　休んだと　おもいます。
I think that Mr./Ms. Kobayashi was absent from school yesterday.

(わたしは)きのう　小林さんは　がっこうへ　行かなかったと　おもいます。
I think that Mr./Ms. Kobayashi did not go to school yesterday./I don't think that Mr./Ms. Kobayashi went to school yesterday.

(わたしは)きのうの　テストは　やさしかったと　おもいます。
I think that the test we had yesterday was easy.

(わたしは)きのうの　テストは　むずかしくなかったと　おもいます。
I think that the test we had yesterday was not difficult./I don't think that the test we had yesterday was difficult.

(わたしは)小林さんは　ずっと　元気だったと　おもいます。
I think that Mr./Ms. Kobayashi was in good health all the time.

(わたしは)小林さんは　びょうきでは　なかったと　おもいます。
I think that Mr./Ms. Kobayashi was not sick./I don't think that Mr./Ms. Kobayashi was sick.