School bells are ringing loud and clear; vacation’s over, school is here” is a school saying that has been printed on several images. The lines are from the short poem “School” by Winifred C. Marshall. It’s not known when the poem first appeared.
 
An obituary in the Arkansas Democrat (Little Rock, AR) on June 3, 1957 (when she died at age 79) stated:
 
“For many years, Mrs. Marshall was a frequent contributor to children’s magazines and wrote short poems for publication.”
 
     
3 June 1957, Arkansas Democrat (Little Rock, AR), “Former Arkansas Writer Is Dead,” pg. 9, col. 3:
Rogers—Mrs. Winifred Catherine Marshall, 79, a former resident of Rogers and sister of Erwin Funk, retired newspaper publisher, died Saturday in the home of her son, Don Marshall, at Pasadena, Calif.
 
Born in Deep River, Ia., she came to Rogers with her parents in 1897. She graduated from the Rogers Academy, was married to John S. Marshall, and moved to Muskogee, Okla., where the couple lived ntil Mr. Marshall’s death in 1945. Two years later she went to Pasadena.
(...)
For many years, Mrs. Marshall was a frequent contributor to children’s magazines and wrote short poems for publication.
 
Google Books
Daily Poetry
By Carol Simpson  
Parsippany, NJ: GoodYear Books
1995
Pg. 58:
School
by Winifred C. Marshall (Reprinted from a book with a 1983 copyright.—ed.)
School bells are ringing, loud and clear;
Vacation’s over, school is here.
 
We hunt our pencils and our books,
And say goodby to fields and brooks.
 
To carefree days of sunny hours,
To birds and butterflies and flowers.
 
But we are glad school has begun,
For work is always mixed with fun.
 
When autumn comes and the weather is cool,
Nothing can take the place of school.
     
Twitter
Sara Campos
@saracampos7
School bells are ringing loud and clear vacation’s over, school is here
11:24 PM - 16 Jan 2013
   
Twitter
Rebecca Saltman
@opendoors4U
Experiencing #JOY Day 299 #School bells are ringing loud and clear; vacation is over, school is here” ~Wini… http://tmblr.co/Z1EZqtsz0h2W
8:43 AM - 22 Aug 2013
   
Twitter
Praveen.G
@pravynair
School bells are ringing loud and clear,vacation’s over,school is here, http://fb.me/6EpE2raXY
2:41 AM - 1 Nov 2013
   
Twitter
United Way of Story County
@LiveUnitedStory
“School bells are ringing loud and clear; vacation’s over, school is here!” -Winifred C. Marshall
4:47 PM - 14 Aug 2014
   
Twitter
Jeaf DjeAfskie Piocnacia
@djeAfskie
“School bells are ringing loud and clear, vacation’s over, school is here.”
- Winifred C. Marshall… http://fb.me/3wOweWrkt
8:48 AM - 2 Sep 2014
     
IOL (South Africa)
School policies need to change to make uniforms accessible
OPINION / 17 JANUARY 2018, 12:11PM / KABELO CHABALALA
‘School bells are ringing loud and clear; vacation’s over, school is here,” said the late novelist and memoirist, Winifred C Marshall. Indeed, school is here, because today is the start of the 2018 school year.
 
Twitter
APenumarthy
@Penumarthy_
School bells are ringing loud and clear; vacation’s over; school is here @BalmoralDrivePs
8:57 PM - 3 Sep 2018