Uncharacteristically for Mary, this photograph is not dated.  However, her daughter (#50) appears to be about 8 years old so I would date it around 1909.  Characteristically, there is a “key” on the back of the photo (see image below).  Those names are transcribed at the bottom of this post.

1. Dora Murphy
2. Mrs. Geo. Larson (Trese or Trise? Betor)
3. Lexie Guilbault
4. Nora Haley
5. [unidentified]
6. Minnie Buselion
7. Mae Touhy
8. Cecil Oconnell [or O’Connell?]
9. Gertie Bakenhall
10. Joe Krouse
11. Harley Bo??ee
12. ?asty Betor
13. Johnie Peabody
14. W?rn Buselion
15. Morgan Langon
16. [unidentified]
17. David Julian
18. [unidentified]
19. Edward Julian
20. Victoria Betor
21. Margaret Tuohy
22. George Loyd
23. Katie Guilbault
24. Draper girls
25.        “         “
26. Selma Winstrom [or Wenstrom?]
27. Catheline Oconnell [or O’Connell?]
28. [unidentified]
29. Lizzie Sullivan
30. Freda Sharp
31. Katie Sullivan
32. Russell Williams
33. [unidentified]
34. Lenord Micheals [or Michaels?] 
35. Frank Hufty
36. Charlie Laiff
37. Arthur Betor
38. Frank Sharp
39. Jack Haley
40. Delore Guilbault
41. Roland Lynch
42. Tom Kirby
43. Joe Oconnell [or O’Connell?]
44. Wilbert ??
45. Tom Laiff
46. Micheal [or Michael?] Tuohy
47. [unidentified]
48. Charles Guilbault
49. Lillian Middlebrooks
50. Frances Schenk [my grandmother]
51. Cathryn Chisolm
52. Edna Murphy
53. Norine Murphy
54. Ruth Lee
55. Draper Girl
56. Freda Ortel
57. Vera Guilbault
58. Mae Haley
59. Nellie Guilbault
60. Emma Horton
61. Chester Chisolm
62. Willie Tuohy
63. [unidentified]
64. Hugh Chisolm
65. [unidentified]
66. Nick Zimmerman
67. Florence Lynch (teacher)
68. Alice Sullivan
69. Sumner Horton
70. Leo. Kirby
71. Yelmer Winstrom [or Wenstrom?]
72. Gertie Bakenhall
73. Florence Guilcrist
74. [unidentified]
75. Mary Krouse
76. Percy Mead
77. Minnie Busilion (teacher)
78. Will Lee
79. [unidentified]