Hi,
I have found these baptisms, with mother Ann,
Thomas GRACE
10 NOV 1793 Studham, Bedford
EDWARD GRACE
08 APR 1798 Studham
JOHN GRACE
30 MAY 1803 Studham, Bedford
It looks like Thomas marries Mary Ann GEORGE,
Thomas GRACE
Mary GEORGE
Marriage: 06 May 1820 Whipsnade, Bedford
This would fit as in 1861 Shadrach JACKSON has an Aunt and Uncle, Ann and Thomas GEORGE living with them.
The 1841 census has,
1841 HO107/5/38 f.4 p.2 & f.5 p.3 Whipsnade
Deadmansey Wood
JACKSON
Thomas 40 Ag Lab
Mary 30
Thomas 20
John 15
Shadric 15
Emma 14
William 12
Edward 10
Sidney 8
Mary 6
David 10 months
All born Bedfordshire apart from Thomas Snr, but it looks like Studham was on the Bedfordshire/Hertfordshire border,
http://www.genuki.org.uk/big/eng/BDF/Studham/index.htmlThen in 1851 they are still JACKSON,
1851 HO107/1757 f.220 p.10 Whipsnade
Deadmoney Wood
JACKSON
Thomas Head 59 Agricultural Labourer Beds Studham
Mary Ann Wife 54 Beds Houghton Regis
Mary Ann Daur 13 Straw Plaiter Beds Whipsnade
David Son 10 " "
but then in 1861 they are GRACE

1861 RG9/1011 f.106 p.1 Kensworth, Hertfordshire
South side of Kensworth
GRACE
Thomas Head Wid 72 Agricultural Labourer Bedfordshire Studham
David Son Un 20 Matter Bedfordshire Whipsnade
So it looks like the GRACE/JACKSON query could come from Shadrach's father Thomas. Do you have Shadrach's marriage certificate to check who is father was?
Regards,
Daisy