Looks like it is a myth that the 100-point scale can be credited to Robert Parker

'LONDON— Robert M. Parker Jr. , widely regarded as the world’s most powerful wine critic, has announced he will no longer taste Bordeaux en primeur.

The Wine Advocate founder, credited as the creator of the 100-point wine rating scale, says the time is right for him to step back from the pressure of reviewing more than 600 wines from barrel.'

It is interesting how certain claims get repeated until they become 'held truths'. Take the nation that Robert Parker was the first to adapt the 100-point scale used in the USA to mark school essays to assess wine. Will Lyons, in yesterday's The Wall Street Journal is only the latest to  repeat this 'fact' – 'credited as the creator of the 100-point wine rating scale'. 

Instead detailed research from the excellent Aaron Nix-Gomez (https://hogsheadwine.wordpress.com/) indicates that the use of a 100-point scale may well predate Robert Parker by some 125 years. So we may well be able to credit Robert with the modern calibration of the 100-point scale but not its creation. There is no doubt that it was Parker who popularised the 100-point scale and made it known around the wine world as that it is now the most used scale.. 

Although it is hardly surprising that a scale used to assess American wines in the mid 19th century didn't immediately grab the wine world's attention, Parker's remarkable and so far unique success is probably due to a blend of right place, right time, his energy and focus plus people's liking for ratings.       

“Assuming 100 to be the standard for best”: The 100-point wine scale predates Robert Parker’s by 125 years
During my recent visit to Albuquerque I came across numerous references indicating that the wines of Bernalillo, located just north of Albuquerque, were celebrated next to those of El Paso in what is now Texas.  One such example appears in Colonel James F. Meline’s account of his summer tour Two Thousand Miles on Horseback (1866).[1] Colonel Meline took time to stop and taste several of the wines in Bernalillo.  He found that the “wines are capable, with proper treatment, of being made excellent” from the “superior” grapes.  Unfortunately, the wine was “inexpertly handled” and “used almost as fast as made”.  Thus old wines were “almost out of the question.”  It was later in Albuquerque that he was able to drink a Bernalillo wine “that was quite as good as any made at El Paso.”

Colonel Meline must have been suitably impressed by the Bernalillo wine he tasted in Albuquerque for he sent two bottles to the American Wine Growers’ Association of Cincinnati, Ohio.  The Association published in its proceedings, which Colonel Meline reproduced in his appendix, that the 1861 white wine received a “vote 90” and the red wine “81.”  According to George Graham, Esquire, President of the Association, the white wine “was considered better than most wines of the same age, either of Catawba or good Rhine wine.”  The wines were judged “by figures marked up to 100, which is the highest character of wine of any kind…Most of our Ohio wine does not reach the excellence of the wine presented to you.”

https://hogsheadwine.wordpress.com/2014/12/31/assuming-100-to-be-the-standard-for-best-the-100-point-wine-scale-predates-robert-parkers-by-125-years/ 

“That we may know the relative value of their own manufacture”:  The spread of the 100-point wine scale in late 19th century America

By the 1850s Ohio was the largest wine producing state in the country with the Catawba vine the mostly widely planted.  These vines soon began to show disease.  In response, the American Wine Growers’ Association of Cincinnati, Ohio set out to find hardier vines that would produce wine just as good as their favorite Catawba.  To evaluate experimental lots of wine the Association developed a 100-point wine scale which they first employed in 1853.  This scale continued to be used by the Association for the rating of all wines through at least 1870.  Ohio was not the only state to employ the 100-point scale.

The spread of the 100-point scale follows the rise of state horticultural societies interested in the cultivation of vineyards and production of wine. The spread appears particularly active in the 1860s.  There was an interest in improving the quality of wine to gain access to the sales market of domestic and foreign wine.  The scale facilitated judging committees in picking the top wines from several dozen samples as well as to compare both within and across tastings.  Judging committees were typically made up of three to five members.  The final score for a wine was simply the average of each judge’s score.  The top wines were then those with the highest final score.'

https://hogsheadwine.wordpress.com/2015/01/06/that-we-may-know-the-relative-value-of-their-own-manufacture-the-spread-of-the-100-point-wine-scale-in-late-19th-century-america/