The following lessons all came from the website Teachers Pay Teachers.  A link to the lesson is provided.  In many cases, these lesson plans are free although we have also included a few inexpensive ideas as well.  

https://www.teacherspayteachers.com/

You can search for other lessons by grade level and subject area.  Just be sure to type in the term "QR Code" to generate a list of activities based on QR Codes.

English (Grades 4-12):  Sentence vs. Fragment Activity:

https://www.teacherspayteachers.com/Product/Sentence-Vs-Fragment-QR-Code-Activity-1006626?st=f4b14aa3ca90fe0dcf1bd42b2522b6f8

English (Grades 9-12):  15 Cell Phone-Based English Activities:

https://www.teacherspayteachers.com/Browse/Search:15%20Cell%20Phone-Based%20English%20Activities:%20qr%20code

Library (Grades 3-7):  QR Code Hunt-Library Edition:

https://www.teacherspayteachers.com/Product/QR-Scavenger-Hunt-in-the-Library-484536?st=9a8aa4bc11b58252bc480bd6971abf79

Math (Grades K-5):  Once Upon a QR Code Math Solving:

https://www.teacherspayteachers.com/Product/Once-Upon-a-QR-Code-technology-integrated-math-center-208763?st=c92160e8a8972332dd48323fbe35b227

Math (Grades 7-10):  QR Codes for Determining Parallel and Perpendicular Lines:

https://www.teacherspayteachers.com/Product/QR-Codes-for-Determining-Parallel-and-Perpendicular-Lines-1591631?st=5c80451ea1aa7089df9cee511c7668e0

Physical Education (Grades 7-12): Flexibility Exercise Classes Stations for PE/Personal Fitness

https://www.teacherspayteachers.com/Product/Flexibility-Exercise-Classes-Stations-for-PEPersonal-Fitness-7971337?st=6e6ae567e44b40b2b12d4e8f1608d3e3

Science:  (Grades 4-7):  Solar System QR Code Scavenger Hunt:

https://www.teacherspayteachers.com/Product/Solar-System-QR-Code-Scavenger-Hunt-478115?st=e40d9662f430e081ab34ff47557da44d

Science:  (Grades-7-12):  Our Solar System:  Device-Based Scavenger Hunt:

https://www.teacherspayteachers.com/Product/Our-Solar-System-Device-Based-Scavenger-Hunt-Activity-Let-the-Hunt-begin-2786454?st=e40d9662f430e081ab34ff47557da44d

Spanish (Grades 9-11):  Spanish Present Tense Regular Verb Conjugations:

https://www.teacherspayteachers.com/Product/Spanish-Present-tense-regular-verb-conjugations-1771080?st=c38e3ae2b417e4e89d6da12bb6eb384f